InvalidIndexError when calling xr.Dataset.drop_isel for dimension with non-unique values

[mliukis]

I have to drop some of the "layers" in Dataset dimension which has non-unique values. When using xr.Dataset.drop_isel I am getting an exception because the dimension has non-unique values.

InvalidIndexError: Reindexing only valid with uniquely valued Index objects

I guess, I am surprised to see the exception as I am specifying exact index positions to drop from the dataset. I could see the reason for the exception if I am to provide dimension labels to drop instead.

Is there a way to "drop" layers for the dimension which has non-unique values in it? Any help is much appreciated!

Here is a code snippet which reproduces the problem (code is borrowed from xarray.Dataset.drop_isel which I slightly modified to have non-unique values):

import numpy as np
import xarray as xr

data = np.arange(8).reshape(2, 4)

labels = ["a", "b", "c", "a"]

ds = xr.Dataset({"A": (["x", "y"], data), "y": labels})
ds.y.values

drop_ds = ds.drop_isel(y=[1, 2])
ds.y.values

drop_ds.y.values

which produces output

array(['a', 'b', 'c', 'a'], dtype='<U1')
---------------------------------------------------------------------------
InvalidIndexError                         Traceback (most recent call last)
<ipython-input-20-6ca9434b3b2f> in <module>
      9 ds.y.values
     10 
---> 11 drop_ds = ds.drop_isel(y=[0, 2])
     12 ds.y.values
     13 

~/anaconda3/envs/itscube/lib/python3.8/site-packages/xarray/core/dataset.py in drop_isel(self, indexers, **indexers_kwargs)
   4347             new_index = index.delete(pos_for_dim)
   4348             dimension_index[dim] = new_index
-> 4349         ds = ds.loc[dimension_index]
   4350         return ds
   4351 

~/anaconda3/envs/itscube/lib/python3.8/site-packages/xarray/core/dataset.py in __getitem__(self, key)
    561         if not utils.is_dict_like(key):
    562             raise TypeError("can only lookup dictionaries from Dataset.loc")
--> 563         return self.dataset.sel(key)
    564 
    565 

~/anaconda3/envs/itscube/lib/python3.8/site-packages/xarray/core/dataset.py in sel(self, indexers, method, tolerance, drop, **indexers_kwargs)
   2346         """
   2347         indexers = either_dict_or_kwargs(indexers, indexers_kwargs, "sel")
-> 2348         pos_indexers, new_indexes = remap_label_indexers(
   2349             self, indexers=indexers, method=method, tolerance=tolerance
   2350         )

~/anaconda3/envs/itscube/lib/python3.8/site-packages/xarray/core/coordinates.py in remap_label_indexers(obj, indexers, method, tolerance, **indexers_kwargs)
    417     }
    418 
--> 419     pos_indexers, new_indexes = indexing.remap_label_indexers(
    420         obj, v_indexers, method=method, tolerance=tolerance
    421     )

~/anaconda3/envs/itscube/lib/python3.8/site-packages/xarray/core/indexing.py in remap_label_indexers(data_obj, indexers, method, tolerance)
    276             coords_dtype = data_obj.coords[dim].dtype
    277             label = maybe_cast_to_coords_dtype(label, coords_dtype)
--> 278             idxr, new_idx = convert_label_indexer(index, label, dim, method, tolerance)
    279             pos_indexers[dim] = idxr
    280             if new_idx is not None:

~/anaconda3/envs/itscube/lib/python3.8/site-packages/xarray/core/indexing.py in convert_label_indexer(index, label, index_name, method, tolerance)
    206                     "MultiIndex variable: " + index_name
    207                 )
--> 208             indexer = get_indexer_nd(index, label, method, tolerance)
    209             if np.any(indexer < 0):
    210                 raise KeyError(f"not all values found in index {index_name!r}")

~/anaconda3/envs/itscube/lib/python3.8/site-packages/xarray/core/indexing.py in get_indexer_nd(index, labels, method, tolerance)
    109     """
    110     flat_labels = np.ravel(labels)
--> 111     flat_indexer = index.get_indexer(flat_labels, method=method, tolerance=tolerance)
    112     indexer = flat_indexer.reshape(labels.shape)
    113     return indexer

~/anaconda3/envs/itscube/lib/python3.8/site-packages/pandas/core/indexes/base.py in get_indexer(self, target, method, limit, tolerance)
   2984 
   2985         if not self.is_unique:
-> 2986             raise InvalidIndexError(
   2987                 "Reindexing only valid with uniquely valued Index objects"
   2988             )

InvalidIndexError: Reindexing only valid with uniquely valued Index objects